1. Field of the Invention
The present invention relates to the field of closed loop lapping systems and more particularly to a novel magnetic resistive head lapping system having electromagnetic actuators effective to correct balance and bow of a workpiece or row tool in response to sensing signals derived from resistive measurements on the workpiece.
2. Description of the Prior Art
Magnetic heads are used extensively in data processing systems, such as disk drives. During head production, batch fabrication is employed whereby a multiplicity of transducers are deposited in a row on a ceramic bar for lapping, polishing and processing simultaneously. The ceramic bar serves as a support or substrate for the transducers and subsequently is divided into head slider elements. During the manufacture of magnetic heads or head sliders with thin film transducers, the pole tips at which the transducing gap is disposed are ground and lapped to achieve a desired throat height at which optimum data signal processing can be realized. The throat height of all the transducers made during a production run for use with a data storage product must be maintained within a defined limited tolerance.
A problem that exists during the lapping process is row bow, which is a condition wherein the ceramic bar is stressed and assumes an undesirable curvature. As a result, the transducer pole tips that encompass the transducing gap are differently aligned relative to the lapping plate and therefore are lapped at different rates. This condition would result in different throat heights for the transducers disposed along the ceramic bar. Prior art lapping systems employ optical guides or electrical lapping guides that indicate changes in the electrical and magnetic characteristics of the head circuit, which are used for implementing manual lapping. The prior art approach is time-consuming, subject to operator error, cannot correct for row bow and does not afford optimum production yield.
Prior attempts to correct for ceramic bar or slider bar distortion is disclosed in U.S. Pat. No. 5,203,119. However, problems have been encountered which stem from the use of a mechanical plunger operable in response to sensed transducer signals to apply pressure to critical locations on the row tool carrying the slider bar. Movement of the plunger and transfer of the loads from the plunger to the row tool are not always accurate enough to achieve desired bending moments in the row tool. Also, no provision is made in prior devices to adjust for balance or tilt of the row tool prior to the lapping procedure.
Therefore, a long-standing need has existed to provide a lapping apparatus which includes means for adjusting for balance and bow of a row tool which is accurate and which eliminates frictional forces normally encountered when employing strictly mechanical pressure-applying techniques. Such a means should include accurate sensing of row tool structural condition with respect to bow or curvature and such signals should be applied to actuating means for applying load transfer moments to the row tool for adjustment purposes.